Production of Asparaginase Enzyme by Aspergillus niger Isolated from Soil

Asparaginase is an enzyme which converts L-asparagine to L-aspartic acid produce asparaginase. Eukaryotic microorganisms like yeast and filamentous fungi such as Aspergillus, Penicillium and Fusarium species, have a potential for L-asparaginase production without side effects. The study was designed to produce Asparaginase by fungi isolated from the soil. Different soil samples were collected from various locations around Uli in the Ihiala Local Government area and used for the isolation of fungi. The fungal isolates were screened for asparaginase production. Thereafter, the best fungal isolates were selected and used for optimisation studies. Pure cultures of the fungi isolates were obtained after repeated subculture on SDA plates. The multivariate regression tests were used as a tool, using SPSS version 25. Among the 43 fungi isolated, 15 were positive for L-apsaraginase production. It was found that fungal isolate wds-8 (from waste dump site soil) produced the highest L-asparaginase yield of 380 U/mL, followed by isolate gds-7 (from garden soil) with 280 U/mL and isolate ccf-3 (from cassava cultivated field soil) with 250 U/mL. The isolate wds-8 was selected as the best producer and was used for further study. It was identified as Aspergillus niger and designated as Aspergillus niger wds-8. Maximum L-asparaginase yield (572 U/mL) by Aspergillus niger wds-8 was observed at an incubation period of 96 h; thereafter, the yield gradually decreased till 168 h. The highest L-asparaginase production corresponded with the dry mass yield of 1.7 g/100 mL. Sucrose stimulated the highest L-asparaginase yield of 655 U/mL, followed by galactose with 503 U/mL. Ammonium sulphate stimulated the highest L-asparaginase yield of 776 U/mL, followed by ammonium chloride with 657 U/Ml. The results of the study show that some asparaginase-producing fungi are present in the soil.